The present invention relates to systems and methods for controlling the amount of cationic coagulant to be introduced into laundry waste water having a content of non-solid fats, oils, and/or grease which is to be reduced.
Laundry waste waters include or become contaminated with one or more fats and/or oils and/or grease. As used herein, the term "FOG" refers to fats and/or oils and/or grease. The FOG content is often present in laundry waste waters in non-solid form, for example, in a liquid emulsified form, such as the discontinuous phase in an aqueous emulsion. For example, the water utilized in a conventional laundry operation becomes contaminated with non-solid FOG, for example, from the articles which are laundered and/or from the detergents and other additives used in the operation. This laundry waste water often cannot be disposed of directly into a publicly owned treatment works because of the relatively high non-solid FOG concentration.
One approach to overcoming this problem has been to add a coagulant, for example, a cationic coagulant such as one or more cationic polymers and the like, to the laundry waste water so as to coagulate and separate at least a portion of the FOG from the laundry waste water. These coagulated materials are separated from the remainder of the laundry waste water and disposed of, for example, as a sludge in a land fill or other suitable disposal facility. The resulting laundry waste water has a sufficiently reduced non-solid FOG concentration to be conveniently disposed of in a publicly owned treatment works.
One potential difficulty with such a treatment process is that the non-solid FOG level in the laundry waste water varies over time so that the demand for cationic coagulant also varies. In general, as the nonsolid FOG level in a laundry waste water increases, the amount of cationic coagulant needed to provide a laundry waste water product having an acceptably low non-solid FOG concentration also increases. Thus, the amount of cationic coagulant used is often set at a relatively high level to insure that the water entering the publicly owned treatment works is acceptable. The amount of coagulant used in this type of process is often in excess of that needed to provide the acceptably low FOG content.
Directly analyzing an aqueous medium for non-solid FOG is often a tedious and time consuming task which may involve taking a sample of the laundry waste water. The time involved in performing these steps may be such as to render the FOG determination obsolete in that the laundry waste water being treated may have a different level of FOG than that determined via this relatively complex procedure.
Martin U.S. Pat. No. 4,855,061 discloses a system for controlling coagulant dosage to water to remove nonsettleable solids, for example, to produce potable water. The coagulant is controlled using a charge sensing means which has a set point that is adjusted in response to the turbidity of the treated water. This patent does not disclose treating relatively heavily contaminated industrial waste waters, such as laundry waste waters, which contain non-solid contaminants, such as non-solid FOG. Also, the disclosed system relies on measuring the turbidity of the finally treated water which adds to the cost and complexity of the system.
German Patent 3,344,275 discloses a system for treating waste waters, such as laundry waste waters, which include non-solid contaminants, for example, non-solid FOG. Various parameters of the raw waste water are measured. Downstream of these measurements, treatment chemicals are added to the waste water. Flocculent is added in response to the cloudiness measured; alkali and/or acid is added in response to the pH measured; and reducing agent is added in response to the redox potential measured. This German patent does not disclose using the electric charge value of the raw waste water to control flocculent addition. The turbidity of the raw waste water may not provide an accurate indication of the amount of flocculent needed. For example, the non-solid FOG may, at this point, be dissolved in the water or be of such small size as to not contribute to turbidity. Thus, ineffective or insufficient flocculent dosing may occur.
Dobrez et al U.S. Pat. 5,246,590 discloses measuring the electric charge of a combination of laundry waste water and cationic coagulant downstream from the introduction of the cationic coagulant. This measured value is used to control the amount of coagulant added. While the systems and methods disclosed in this patent are very effective in controlling the amount of cationic coagulant used, certain concerns remain. For example, since the electric charge value is measured after cationic coagulant is added, the partially coagulated mixture contacting the probe of the electric charge detector has a tendency to foul or dirty the probe with the coagulated solids. This can result in unreliable and inconsistent measurements and control, and may require relatively frequent cleaning of the probe, during which the control system is not operating. In addition, changes in the amount of coagulant added occur reactively, that is after the mixture being measured includes all the coagulant it will ever have. No additional coagulant is introduced into (and no coagulant can be withdrawn from) this mixture as a result of these measurements. In this sense, such control systems are not optimally effective.